Method and apparatus for a configurable metal register

ABSTRACT

A configurable metal register of an integrated circuit that allows a register output value to be changed by changing any metal or any contact within a metal pattern solution of the register. More than one metal and/or corresponding contact within the metal pattern solution may be changed so that the register output value is correspondingly changed.

TECHNICAL FIELD

[0001] This invention relates generally to the field of integratedcircuit devices, and more specifically to registers of integratedcircuits.

BACKGROUND OF THE INVENTION

[0002] The design of complex integrated circuits (ICs), such as CentralProcessor Unit (CPU) chips, normally goes through several revisions, orturns, in silicon before the final production version is ready. Theserevisions could be a full turn, which includes metals and FET's, or ametal only turn in which only metal layers of the chip are changed.Fabrication of these turns is costly. As an example, for a current CPU,a full turn may cost on the order of one million dollars while a metalonly turn may cost on the order of half a million dollars. A turn with asmaller number of metal layers changed (a partial metal turn) costsless. The cost is roughly proportional to the number of metal layerswith its associated contacts, with lower level metal costing more.Reducing the number of metal layers that need to be changed helps toreduce the cost of fabrication. As an example, a design chip's firstturn may only change one metal layer with the metal layer's associatedcontact.

[0003] The front side bus is the portion of an integrated circuit (IC)that is responsible for transporting data among the various subsystemsand devices that make up the IC. In many integrated circuitapplications, the performance of the front side bus of the integratedcircuit is controlled by a collection of registers. As bus speedincreases and the number of chips on the bus increase, the signalintegrity of bus signals becomes more important. That is why manyregisters may be added to the CPU to change the associated busparameters, such as driver termination, driver slew rate, receiver trippoint, receiving deglitch delay, etc.

[0004] When the IC is in the design stages, it may undergo iterations ofchanges to the register values, where each iteration can require thefabrication of a new prototype IC. For each revision of the IC, theinput/output performance of the front side bus of the IC is tested. Ifthe bus performance does not meet design guidelines, then the IC layoutis altered and a new IC revision fabricated. Clearly, the turnaroundtime of this process can be lengthy and affect the overall design timeof the IC. Conversely, it can be seen that for an IC already in aproduction environment, having registers set to incorrect values can becatastrophic to the IC operation. This situation may occur if the designand prototyping was not done properly or it may be due to unforeseensystem level impacts.

[0005] Referring now to FIG. 1, a block diagram of a fabrication process100 for a circuit containing one or more registers is shown. After an ICcontaining one or more registers is designed (block 110), the IC isfabricated for testing (block 120). The IC is then tested for layouterrors (block 130). If the IC test fails (block 140), then the registervalues must be changed during IC layout and the IC fabricated and testedagain (blocks 120 and 130). The number of times the registers arechanged, the layout changed and the IC fabricated and re-tested has alarge impact on the overall cost and time-to-market of the IC. A secondconcern can occur if the IC passes the pre-production test and entersthe production process (block 150). If an error is detected after the ICis in production (block 155), either due to a design flaw or an error inthe previous test process of block 130, then the IC's that have beenproduced may not be usable, the IC layout will need to be modified(block 145) and the IC fabricated and tested again (blocks 120 and 130).Clearly detection of an error after production has started isundesirable, since many IC's may be wasted.

SUMMARY

[0006] Therefore, in accordance with certain embodiments of the presentinvention, in an integrated circuit structure of the present invention,a metal pattern solution provides that a change in the metals or thecontacts of the metal pattern solution causes an output value of aregister to change. Modifying the metal pattern solution, which iscoupled to the register, by changing any of the metals or the contactsoperates to modify the output value of the register. In accordance withcertain other embodiments of the present invention, the metal patternsolution is coupled to a metal switching tower, which is then coupled toground and coupled to a multiplexer (mux). The mux is coupled to aplurality of inputs and uses a selection input from the metal switchingtower to select an appropriate output value of the register. The outputvalue of the register is coupled to a control signal that controls thevalidity of the output value, thereby saving power. A focused ion beam(FIB) may be used to sever the connection between the metal switchingtower and ground, causing the selection input to change value. Hence theoutput value of the register may be affected by the action of the FIB.According to a method consistent with certain embodiments of the presentinvention, an output value of a register of a plurality of registers ofan integrated circuit structure may be configured by changing one ormore of a plurality of metals and a corresponding plurality of contactsin a metal pattern solution of the integrated circuit structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The features of the invention believed to be novel are set forthwith particularity in the appended claims. The invention itself however,both as to organization and method of operation, together with objectsand advantages thereof, may be best understood by reference to thefollowing detailed description of the invention, which describes certainexemplary embodiments of the invention, taken in conjunction with theaccompanying drawings in which:

[0008]FIG. 1 is a block diagram of a fabrication process for a circuitcontaining one or more registers, according to the prior art.

[0009]FIG. 2 is a circuit diagram of a configurable metal register,according to a certain embodiment of the present invention.

[0010]FIG. 3 is a metal pattern solution example of the metal pattern ofa flexible metal register, according to a certain embodiment of thepresent invention.

[0011]FIG. 4 is a block diagram of a process for changing one or moreregister values by changing a metal pattern, according to a certainembodiment of the present invention.

[0012]FIG. 5 is a flow diagram for a process of changing a registervalue using a focused ion beam (FIB), according to a certain embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] While this invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail specific embodiments, with the understanding thatthe present disclosure is to be considered as an example of theprinciples of the invention and not intended to limit the invention tothe specific embodiments shown and described. In the description below,like reference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

[0014] Referring now to FIG. 2, a circuit diagram 200 of a configurablemetal register structure is shown, according to a certain embodiment ofthe present invention. Input INO 225 is the default output of mux 235because of a coupling of mux selection 220 to ground 215 through the useof Metal Switching Tower 210. In a certain embodiment of the presentinvention, Metal Switching Tower 210 is coupled to Vdd 240. After afocused ion beam (FIB) 217 cuts the connection of mux selection 220 toground 215, mux selection 220 becomes high (or one) by the weak pull-updevice 250 when the POWUP control signal 245 is zero. In a certainembodiment of the present invention, FIB 217 is not present, and theconnection of mux selection 220 to ground 215 is controlled externally.After the mux selection 220 becomes 1, input IN1 230 is chosen by mux235 as the output 240. In a certain embodiment of the present invention,a complimentary value of input IN1 230 is chosen as the output 240 ofmux 235. The output 240 of mux 235 is latched by the rising edge ofPOWUP control signal 245. It is noted that the output 240 of mux 235 maybe latched by the falling edge of POWUP control signal 245 withoutdeparting from the spirit and scope of the present invention. In acertain embodiment of the present invention, the POWUP control signal245 is operable to save power during normal operation of a chip having ametal pattern solution.

[0015] Referring now to FIG. 3, a metal pattern solution example 300 ofa configurable metal register structure as may reside within MetalSwitching Tower 210 is shown, according to a certain embodiment of thepresent invention. A metal pattern solution in this example isrepresented by a plurality of metal/contact layers: metal/contact M4340, metal/contact M5 330, metal/contact M6 320, metal/contact M7 310.The plurality of metal/contact layers are shown in four configurations,illustrated in FIG. 3 as four columns (350, 355, 360, 365). It is notedthat other metal layers may be present in the metal pattern solutionwithout departing from the spirit and scope of the present invention.The checkered metals of FIG. 3 represent a coupling of a metal to asupply voltage VDD, while the clear metals of FIG. 3 represent acoupling of a metal to a ground. The checkered metals and the clearmetals of FIG. 3 further contain contacts, illustrated as small blacksquares, that are operable to couple the checkered metals and the clearmetals to other metal layers in the metal pattern solution. In metalpattern solution example 300, metal/contact M4 340 has output value 220,used as the mux select in FIG. 2, that is 0 during an initialconfiguration of the metal pattern solution. The initial configurationis illustrated in the first column 350 of FIG. 3. The metal patternsolution is housed within switching tower 210.

[0016] In a second configuration of the metal pattern solution the metalof M6 320 is changed. It is noted that in certain embodiments of thepresent invention this change, which occurs during a fabrication of themetal pattern solution, may occur at a later time after the initialconfiguration of first column 350. It is further noted that a designprocess may also be structured so that the configurations represented asthe four columns (350, 355, 360, 365) occur concurrently using fourfabrications of the metal pattern solution. Changing the metal of M6 320causes metal layers (M5 330, M4 340) below metal M6 320 to invert theirrespective voltage orientation, thereby causing output value 220 of M4340 to change from 0 to 1. The metal configuration after the change ofM6 320 is illustrated as the second column 355 of FIG. 3.

[0017] During a third stage, the metal of M5 330 is changed, causingmetal layer M4 340 below metal M5 330 to invert its voltage orientation.The inversion of the voltage orientation causes the output value 220 ofM4 340 to be 0. The metal configuration after the changing M5 330 isillustrated as the third column 360 of FIG. 3. Finally, during a fourthstage, a contact change between M5 330 and M4 340 causes the outputvalue 220 of M4 340 to be 1. The metal configuration after changing thecontact of M4 340 is illustrated as the fourth column 365 of FIG. 3. Ina certain embodiment of the present invention, each change of a metal ora contact of the metal pattern is followed by a fabrication of the metalpattern solution within an IC. The metal pattern solution example 300shows that changing any metal of metal pattern solution or changing anycontact of metal pattern solution can change an output value of aregister containing a metal pattern solution.

[0018] It is noted that one of skill in the art will recognize thatwhile this exemplary metal pattern is shown with four layers, a greateror fewer number of layers could be used without departing from thespirit and scope of the present invention. It is further noted that theorientation of the metals and contacts within the metal pattern solutionmay be configured as desired without departing from the spirit and scopeof the invention, and does not impact the ability of the configurableregister to allow a user to change a register value by changing one ormore metals or one or more contacts of the metal pattern solution.

[0019] Referring now to FIG. 4, a flow diagram of a process for changingone or more register values and one or more contacts 400 is shown,according to a certain embodiment of the present invention. After an ICcontaining one or more registers and one or more contacts is designed(block 410), the IC is fabricated for testing (block 420). The IC isthen tested for layout errors (block 430). In the certain embodiment ofthe present invention, the IC test measures the signal integrity of asignal of one or more signals in the IC. If the IC test fails (block440), then one or more register values and one or more contacts may bechanged during IC layout and the IC is tested again (blocks 420 and430). The one or more register values and the one or more contact valuesmay be adjusted through the use of a metal pattern solution as in block445. It is noted that the metal pattern solution of FIG. 3 and theconfigurable register shown in FIG. 2 containing the same are operableto change the one or more register values and the one or more contactvalues without departing from the spirit and scope of the presentinvention. Referring again to FIG. 4, if the IC test of signal integrityis satisfactory, then the IC may be ready for production or testing ofother modules (block 450). The metal pattern solution allows any metalor contact in any layer of the metal pattern solution to be changed tochange an output register value of the one or more registers. In acertain embodiment of the present invention, the one or more registervalues and one or more contacts are chosen so that the signal integrityis maximized. It is noted that in alternative embodiments, other metricscould be used such as throughput, minimum number of test cycles, etc. Inthe diagram of FIG. 4, the use of a metal pattern solution that allowsany metal change or contact change to change a register value of the oneor more registers reduces fabrication costs. The fabrication costincreases as more metal layers are changed. Since the one or moreregisters do not require any particular metal layer, if a circuitcomprising the one or more registers needs a particular layer, then theone or more registers would preferably just use that metal layer, sothat the number of metal layers that need to be changed does notincrease. If only the one or more registers need to be changed, then acheaper layer could be chosen. In certain embodiments of the presentinvention, lower layers are more expensive than upper layers.

[0020] If a chip has been fabricated and does not work correctly becauseof incorrect register settings, a technique that allows the IC tooperate while the register setting is being adjusted and re-fabricatedwould reduce the amount of time required for testing. Referring now toFIG. 5, a flow diagram for a process of changing a register value usinga focused ion beam (FIB) 500 is shown, according to a certain embodimentof the present invention. After an IC has been designed and fabricated(block 510 and block 520), testing or operational use may determine thatthe IC register values are set incorrectly (block 530). If the registervalues are set incorrectly, then a focused ion beam (FIB) may be used tocut a connection that then toggles the value of the register (block540). This allows this IC to be used, while the error in the registerdesign is corrected (block 545). Note that this technique could be usedto speed the time required to test an IC, or could be used in caseswhere an IC is in production and either design error or compatibilityissues require a different register setting. In a certain embodiment ofthe present invention, a FIB is used to sever the connection between muxselection 220 and ground 215.

[0021] While the invention has been described in conjunction withspecific embodiments, it is evident that many alternatives,modifications, permutations and variations will become apparent to thoseof ordinary skill in the art in light of the foregoing description.Accordingly, it is intended that the present invention embrace all suchalternatives, modifications and variations as fall within the scope ofthe appended claims.

What is claimed is:
 1. A structure operable to configure an output valueof a register of one or more registers of an integrated circuitstructure, said structure comprising a pattern coupled to the registerthat comprises a plurality of metals and a plurality of contacts coupledto said plurality of metals, wherein modifying said pattern by changingone or more of the plurality of metals and the plurality of contactsmodifies the output value of the register.
 2. The structure inaccordance with claim 1, wherein a change in a metal of the plurality ofmetals produces a corresponding change in the output value.
 3. Thestructure in accordance with claim 1, wherein a change in a contact ofthe plurality of contacts produces a corresponding change in the outputvalue.
 4. The structure in accordance with claim 1, wherein successivechanges to one or more metals of the plurality of metals producecorresponding alternating values in the output value.
 5. The structurein accordance with claim 1, wherein successive changes to one or morecontacts of the plurality of contacts produce corresponding alternatingvalues in the output value of the register.
 6. The structure inaccordance with claim 1, wherein the output value is coupled to acontrol signal and wherein said control signal is operable to conservepower of the integrated circuit structure by limiting the amount of timethe output value is valid.
 7. The structure in accordance with claim 6,wherein the output value is coupled to a rising edge of the controlsignal.
 8. The structure in accordance with claim 1, wherein theregister is coupled to a ground potential, and a focused ion beam (FIB)is operable to sever the coupling to the ground potential so that theoutput value of the register is changed.
 9. The structure in accordancewith claim 8, wherein the register is coupled to ground via a selectioninput coupled to a mux at a first terminal and coupled to a metalswitching tower at a second terminal, said metal switching towercomprising the plurality of contacts and the plurality of metals. 10.The structure in accordance with claim 9, wherein the selection input isoperable to choose the output value from one of a plurality of inputs tothe mux.
 11. An integrated circuit structure, comprising: a register ofa plurality of registers of the integrated circuit structure; and apattern coupled to the register, said pattern comprising a plurality ofmetals and a plurality of contacts coupled to said plurality of metals,wherein an output value of the register is changed by modifying one ormore of the plurality of metals and the plurality of contacts of saidpattern.
 12. The structure in accordance with claim 11, whereinsuccessive changes to one or more metals of the plurality of metalsproduce corresponding alternating values in the output value.
 13. Thestructure in accordance with claim 11, wherein successive changes to oneor more contacts of the plurality of contacts produce correspondingalternating values in the output value of the register in the outputvalue.
 14. The structure in accordance with claim 11, wherein the outputvalue is coupled to a control signal, and wherein said control signal isoperable to conserve power of the integrated circuit structure bylimiting the amount of time the output value is valid.
 15. The structurein accordance with claim 14, wherein the output value is coupled to arising edge of the control signal.
 16. The structure in accordance withclaim 11, wherein the register is by default coupled to a groundpotential, and a focused ion beam (FIB) is operable to sever thecoupling to the ground potential so that the output value of theregister is changed.
 17. The structure in accordance with claim 16,wherein the register is coupled to ground via a selection input coupledto a multiplexer at a first terminal and coupled to a metal switchingtower at a second terminal, said metal switching tower comprising theplurality of contacts and the plurality of metals.
 18. The structure inaccordance with claim 17, wherein the selection input is operable tochoose the output value from one of a plurality of inputs to the mux.19. An integrated circuit structure, said structure comprising: a metalswitching tower, coupled to a ground and to a supply voltage, wherein aconnection to the ground is operable to be cut by a focused ion beam(FIB); a mux device, coupled to the metal switching tower by a selectioninput, and further coupled to a transistive device; one or more inputscoupled to the mux device; one or more outputs, coupled to the muxdevice, wherein the one or more outputs are selected from the one ormore inputs in accordance with the selection input; and a control signalcoupled to the transistive device, said control signal operable todetermine the absence or presence of the one or more outputs of the muxdevice.
 20. The structure in accordance with claim 19, wherein cuttingthe connection by the FIB causes at least one of the one or more outputsto change value.
 21. The structure in accordance with claim 19, whereinthe transistive device is a PFET transistor.
 22. The structure inaccordance with claim 19, wherein the metal switching tower furthercomprises a pattern coupled to the metal switching tower, said patterncomprising a plurality of metals and a plurality of contacts, andwherein modifying said pattern by changing one or more of the pluralityof metals and the plurality of contacts modifies an output of the one ormore outputs.
 23. The structure in accordance with claim 22, wherein anymetal of the plurality of metals can be changed to produce acorresponding change in the output.
 24. The structure in accordance withclaim 22, wherein any contact of the plurality of contacts can bechanged to produce a corresponding change in the output value.
 25. Thestructure in accordance with claim 22, wherein successive changes to oneor more metals of the plurality of metals produce correspondingalternating values in the output value of the register.
 26. Thestructure in accordance with claim 19, and wherein said control signalis operable to conserve power of the integrated circuit structure bylimiting the amount of time the output value is valid.
 27. The structurein accordance with claim 26, wherein the output value is coupled to therising edge of the control signal.
 28. A method for controlling anoutput value of a register of a plurality of registers of an integratedcircuit structure, comprising: controlling a metal pattern solution ofthe integrated circuit structure, wherein the metal pattern solution isoperable to change the value of the output value, further comprising:changing one or more of a plurality of metals and a correspondingplurality of contacts of the metal pattern solution.
 29. The method inaccordance with claim 28, wherein the output value toggles between twostates.
 30. The method in accordance with claim 28, wherein afterchanging one of the plurality of metals and the plurality of contacts,applying the register output value to test a signal integrity of theintegrated circuit structure.
 31. The method in accordance with claim30, wherein the signal integrity is the signal integrity of a front-sidebus architecture, and successively changing the plurality of metals andthe plurality of contacts is operable to select an appropriate signalintegrity of the front-side bus architecture.
 32. The method inaccordance with claim 30, wherein if the signal integrity is invalid,changing one of the plurality of metals and the plurality of contacts toeffect the change in the output value of the register of the pluralityof registers.
 33. The method in accordance with claim 28, wherein if theregister output value is incorrect, cutting a connection of a metalswitching tower containing the plurality of metals of the plurality ofcontacts with a ground by focused ion beam (FIB), thereby causing theregister output value to toggle.
 34. The method in accordance with claim33, wherein toggling the register output is caused by a change in aselection input that is coupled to a multiplexer that controls theoutput value.
 35. The method in accordance with claim 28, wherein theoutput value is coupled to a control signal, said control signaldetermining when the output value is valid.
 36. The method in accordancewith claim 35, wherein the output value is latched on the rising edge ofthe control signal.
 37. An integrated circuit structure, comprising: aregister of a plurality of registers of the integrated circuitstructure, wherein the register comprises a metal pattern; and a meansfor controlling an output value of the register by modifying aconfiguration of the metal pattern.
 38. The structure of claim 37,wherein the means for controlling an output value of the registercomprises: the metal pattern comprising a plurality of metals and aplurality of contacts coupled to said plurality of metals, wherein theoutput value of the register is changed by modifying one or more of theplurality of metals and the plurality of contacts of said metal pattern.